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Biomedical subjects

B M Rigor

Publications and source records attributed to B M Rigor.

At least 55 records · Page 3Linked to original sources
PubMed1986

Adaptation of adult brain tissue to anoxia and hypoxia in vitro.

The rat hippocampal slice preparation was used in the present study to demonstrate the ability of adult brain tissue to adapt to anoxic and hypoxic conditions. Adaptation was induced by pre-exposure of hippocampal slices to a short (5 min) anoxic episode. The evoked electrical activity of pre-exposed slices recovered from a subsequent, longer anoxic insult, while that of controls (without pre-exposure), receiving the same insult, did not. The adaptation process is time-dependent; an interval of 0.5 h between the pre-exposure and the subsequent anoxic insult allowed slices to resist anoxic periods of 13 +/- 2 min while after an interval of 2 h an anoxic period of 16 +/- 2 min could be tolerated. Evoked electrical activity persisted in adapted slices during exposure to hypoxia while their non-adapted controls exhibited synaptic silence under hypoxic conditions.

Adaptation, Physiological↗
PubMed1986

Effect of electrical stimulation on the viability of the hippocampal slice preparation.

Continuous electrical stimulation of rat hippocampal slices at a frequency of 1 Hz brought about a 50% decline in the evoked population spike amplitude at a rate 5 times faster than that caused by very low frequency (1/600 Hz) stimulation. Within 2 hr after the high frequency stimulation began the evoked response totally disappeared. By contrast low frequency stimulated slices maintained an evoked response for at least 9 hr. Continuous electrical stimulation, especially at high frequency seems to facilitate the deterioration of the in vitro hippocampal slice preparation.

Animals↗
PubMed1986

Lidocaine depresses synaptic activity in the rat hippocampal slice.

The direct effect of the local anesthetic lidocaine was studied using the hippocampal slice preparation in order to assess the involvement of this structure in lidocaine-induced seizure activity. Changes in the evoked field potential amplitude and latency were used to measure the effect of the drug. A dose-dependent depression of the evoked field potentials was observed at lidocaine concentration of 10(-4)M and greater. No synchronized population bursting (seizures) was observed at any of the concentrations tested (10(-6)M to 10(-3)M). However, the hippocampal slice preparation is capable of producing seizure activity, as was demonstrated following application of penicillin G. The results suggest that the hippocampus is not the site of lidocaine-induced seizure activity.

Animals↗
PubMed1985

Prolonged daily inhalation of halothane modifies the dose-response pattern to acute administration of halothane. An electrophysiological study.

Sensory-evoked field potentials were obtained from freely moving rats implanted sterotaxically with permanent electrodes in the parafasciculus thalami (PF), mesencephalic central gray (CG), ventromedial hypothalamus (VMH) and somatosensory cortex (SCX). Animals were exposed to chronic, subanesthetic inhalation of halothane (0.5%, 3 hr/day, 5 days/week) for 56 days. The averaged acoustic evoked responses (AAER) were recorded on day 0, as well as at 28 and 56 days after a 48-hr halothane-free period ("control") and after acute doses of halothane (0.25, 0.5 and 1.5%). In general, the averaged sensory-evoked responses from each structure were affected at day 0 of the experiment in dose-response manner, and suppression of the responses was the main effect of halothane. Chronic exposure to subanesthetic inhalation of halothane produced marked alteration of the "control" recording from 3 CNS structures; mainly from the mesencephalic central gray, the parafasciculus thalami and the somatosensory cortex and the direction (increase or decrease) of the averaged acoustic evoked responses in all the four CNS sites studied. The total responsiveness was modified as well, i.e. the recordings obtained from the mesencephalic central gray and somatosensory cortex exhibited hypersensitivity while the recordings obtained from the parafasciculus thalami and ventromedial hypothalamus exhibited tolerance. It is concluded that prolonged and intermittent inhalation of halothane can alter the electrophysiological properties of the four structures investigated.

Acoustic Stimulation↗
PubMed1985

A dual chamber for comparative studies using the brain slice preparation.

A dual linear-flow chamber for comparative studies using brain slices is described. Electrophysiological and ultrastructural analysis of rat hippocampal slices incubated in the chamber showed that its two compartments allows performance of reliable paired comparison studies in a highly efficient manner.

Anaerobiosis↗
PubMed1985

Dose effects of halothane on sensory evoked responses obtained from the cortex, reticular formation and central gray.

Sensory evoked field potentials were recorded from the mesencephalic reticular formation (MRF), central gray (CG) and somatosensory cortex (SCX), following incremental doses of halothane in freely-moving rats. Halothane concentrations of 0.25%, 0.5% 1.0% and 2.0% were used. In general, the responses from each structure were affected in dose response manner. The averaged acoustic evoked responses (AAER) exhibit more sensitivity to halothane than the averaged visual evoked responses (AVER). The evoked response and its components obtained from each structure were affected differently by halothane mainly following the initial two halothane doses, (0.25% and 0.5%); mainly increase in amplitude was observed in the recording obtained from the MRF, decrease in the CG, and mixed (increase and/or decrease) in SCX. The degree of the depression of the sensory evoked responses was directly correlated to the level of anesthesia as assessed by sural nerve stimulation.

Animals↗
PubMed1984

Cannabis extract, but not delta 1-tetrahydrocannabinol, inhibits human brain and liver monoamine oxidase.

Mitochondrial monoamine oxidase (MAO) of human brain and liver was inhibited by low concentrations of cannabis extract (CE) and a cannabinoid fraction isolated from it. delta 1-Tetrahydrocannabinol (THC) did not elicit any inhibitory effect on the enzyme. The inhibition of MAO activity by CE and by its active fraction was more pronounced when the monoamine substrates 2-phenylethylamine (PEA) and benzylamine (BA) were used, as compared to the inhibition of the enzyme activity when 5-hydroxytryptamine was the substrate. The active cannabinoid fraction was found to be more potent than CE in inhibiting the activity of MAO with either substrate. The isolated fraction contains at least two cannabinoids with Rf values of 0.67 and 0.71 on silica gel thin layer chromatography (TLC), as determined with toluene/chloroform/methanol (100:10:1, by volume) as the solvent system. The findings of this study emphasize the need for further exploration of the potential of cannabis as a source for therapeutic agents.

Brain↗
PubMed1983

The cholinergic system in rat striatum during morphine tolerance and dependence.

Male Sprague-Dawley rats were used in the present study to assess the effects of chronic treatment of morphine on the striatal cholinergic system. The results demonstrate that neither short nor long-term morphine treatment had an effect on choline acetyltransferase (ChAT) activity or 3H-quinuclidinylbenzilate (3HQNB) binding in discrete striatal regions of the rat brain.

Acetylcholine↗
PubMed1983

Various inputs modify caudate neuronal activity.

This study investigates the input of substantia nigra (SN), dorsal raphe (DR), and medial lemniscus (ML) on caudate nucleus (CN) neurons as well as a non-specific-polysynaptic input (acoustic AC). Ninety-one units demonstrating spontaneous activity were recorded extracellularly using anesthetized rats. SN, DR, ML, and AC stimulation altered the spontaneous discharges in 79%, 90%, 86%, and 85% of the CN neurons, respectively. Only ML stimulation elicited patterns of time-locked responses in 16% of the CN units. The CN neurons showed high convergence to the four types of stimulation. Based on these results, interconnections and interrelations between SN, DR, ML, and the CN are suggested.

Animals↗
PubMed1982

Electrophysiological support in favor of multiple opiate receptors in the caudate and the central gray of the rat.

1. The present study compares the direct actions of morphine on two brain sites known to be rich in opiate receptors, namely, the caudate nucleus and the central gray. Recordings and morphine injections were made through a multibarrel glass micropipette using microiontophoresis. 2. Four different patterns of neuronal response to increasing currents of morphine were recorded in both brain regions. 3. Differences in the response to morphine between the two sites were detected in morphine-dependent rats. While the caudate neurons exhibited super-sensitivity to morphine, the neurons in the central gray displayed tolerance, and in some instances, dependence was evident when naloxone was administered. 4. The distribution of spontaneously active neurons within these two brain areas was found to be different in morphine-naive and morphine-dependent rats. 5. The electrophysiological findings of this study support the hypothesis of multiple opiate receptors.

Animals↗
PubMed1982

Caudate neuronal response to microiontophoretically injected morphine in naive and morphine-dependent rats.

1. The response of caudate nucleus neurons to morphine was found to be dose-dependent and could be divided into two classes: neurons which responded monophasically either by increase or decrease in their firing rate, and neurons whose response can be described as biphasic, exhibiting increase followed by decrease in their firing rate or vice versa, with the increase in morphine concentration. These responses were found in both naive and morphine-dependent rats. 2. Naloxone antagonized the effects of morphine in 74 out of 102 neurons tested. 3. Caudate neurons of morphine-dependent rats showed super-sensitivity to morphine compared to naive rats. 4. Differences were found in the distribution of the spontaneously active neurons between naive and morphine-dependent rats, indicating the existence of two different opiate receptor populations within the caudate nucleus.

Animals↗
PubMed1982

Cardiovascular effects of hypotension induced by adenosine triphosphate and sodium nitroprusside on dogs with denervated hearts.

Adenosine triphosphate (ATP) and sodium nitroprusside (SNP) are administered to patients to induce and control hypotension during anesthesia. SNP is authorized for clinical use in USA and UK, and ATP is clinically used in other countries such as Japan. We investigated how these two drugs act on the cardiovascular systems of 20 dogs whose hearts had been denervated by a procedure we had devised. ATP (10 dogs) or SNP (10 dogs) was administered to reduce mean arterial pressure by 30% to 70% of control. Before, during and after induced hypotension, we measured major cardiovascular parameters. Hypotension induced by ATP was accompanied by significant decreases in mean pulmonary arterial pressure (p less than 0.001), central venous pressure (p less than 0.001), left ventricular end-diastolic pressure (p less than 0.001), total peripheral resistance (p less than 0.001), rate pressure product (p less than 0.001), total body oxygen consumption (p less than 0.05), and heart rate (p less than 0.001); all these variables returned normal within 30 min after ATP was stopped. Cardiac output did not change. During hypotension produced by SNP similar decreases were observed in mean pulmonary arterial pressure (p less than 0.01), central venous pressure (p less than 0.001), left ventricular end-diastolic pressure (p less than 0.01), total peripheral resistance (p less than 0.001), rate pressure product (p less than 0.001), and oxygen content difference between arterial and mixed venous blood (p less than 0.05), while heart rate (p less than 0.001) and cardiac output (p less than 0.05) were increased. Recoveries of heart rate and left ventricular end-diastolic pressure were not shown within 60 min after SNP had been stopped. Both ATP and SNP should act on the pacemaker tissue of the heart.

Adenosine Triphosphate↗
PubMed1981

Halothane accumulation in rat brain and liver.

Halothane concentrations (microgram/g wet weight) was measured in rat brain and liver following exposure to various concentrations of halothane in air. Because of the difficulty of determining the amount of a volatile compound in brain, we analyzed tissue fixed by two different methods. The apparent concentration of halothane in brain was higher following direct decapitation into liquid nitrogen, than after decapitation, removal of fresh tissue, and then freezing. However, the relative effects of altering the inspired concentration were essentially the same in each case. Thus, absolute quantitative accuracy remains a point for discussion; however, we can reach several conclusions regarding the relative accumulation of halothane in brain tissue following various conditions of exposure. Resultant tissue concentrations of halothane were not linearly related to ambient concentrations. Above an inspired concentrations of 1.0%, an increase to 1.5% inspired concentration caused little further increase in the halothane concentration in brain, although the liver concentration increased in proportion to the dose increase. Below an inspired concentration of 0.5%, tissue concentrations were less expected, probably as a result of metabolic degradation occurring at a rate that becomes more noticeable at lower inspired concentrations. Body size was shown to be an important variable affecting the time required for each tissue to reach equilibrium at a given inspired concentration. These data indicate that tissue concentrations at low exposure levels may be less than proportional at dose and that concentrations in small laboratory animals may be expected to exceed values in humans under equivalent conditions of exposure.

Animals↗
PubMed1981

A special holder allows replacement of the recording barrel of a 'piggy-back' multibarrel microelectrode.

A new form of multibarrel micropipette is described. The special holder has several advantages: it can be quickly replaced if it is damaged; the multi-barrel injection portion of the pipette and the drugs it contains can be reused; contamination by spill-over of drugs from one barrel to another is prevented and pressure techniques can be applied using this micro-electrode.

Electrodes↗
PubMed1981

Periaqueductal gray neurons response to microiontophoretically injected morphine in naive and morphine-dependent rats.

The attempt of this study was to investigate the direct effects of increasing doses of morphine on the neuronal activity of the periaqueductal gray in morphine-naive and morphine-dependent rats. The microiontophoresis technique was used for this purpose. The four different responses induced by morphine exhibited dose-related patterns. Naloxone antagonized these responses in about 40% of the cases. Differences were found in the sensitivity of the neurons of morphine between naive and morphine-dependent rats. The phenomena of acute tolerance, chronic tolerance and dependence have been found. The results of this study indicate the presence of different neural populations in the periaqueductal gray in relation to their response to morphine, supporting the notion that subpopulations of opiate receptors exist within this brain area.

Animals↗
PubMed1981

Altered caudate nucleus field potentials following sustained stimulation to different substantia nigra regions.

Evoked potential recording techniques were used as a physiological tool for electrode placement into the substantia nigra pars compacta (SNpc). It was found that when the recording electrodes were implanted at the level of the caudate nucleus (CN), typical patterns were obtained only when the stimulation electrode was located in the SNpc. When the stimulation electrode was fixed in the SNpc and four electrodes were simultaneously used to record depth profile from the caudate nucleus and the septum, the typical responses following stimulation were obtained only when electrodes were within the CN head. High frequency stimulation of the SNpc, which is known to alter dopamine content within the CN, caused a reversible diminution of responses in CN for 5-10 min. This observation was discussed in terms of terminal transmitter depletion.

Animals↗